Aviation & Aeronautics
Intermediate

Mach Number

Ratio of true airspeed to the local speed of sound.

Formula

M=vaM = \dfrac{v}{a}

Variables

MMach number
vTrue airspeed
aSpeed of sound

Example

At Mach 0.85 an airliner flies at 85% of the local speed of sound.

Did You Know?

Mach 1 is the speed of sound — about 1,235 km/h at sea level, but slower up high where it's colder.

machspeedcompressibility